The development of a depth control system for a peat milling machine, part I: sensor development

A closed-loop control system to alleviate the problems of variation in the layer thickness of a milled peat crop (crop depth) has been developed for a peat milling machine (miller). The main enabling technology behind the system, an electromechanical sensor developed to give real-time measurement of crop depth, is designed to act as the feedback element in the control system. The sensor is an accurate predictor of the average crop depth across the miller's 6.5 m width (co-efficient of determination, R-2 of 0.75). The miller, the bog and automatic control system were modelled, and experiments were carried out to establish a topographic model of the bog surface, and an oscillator was specially designed and developed to establish dynamic properties of the bog, for the model. The mean linear spring and damper values thereby measured are 117 kN m(-1) and 1036 Ns m(-1), respectively, for the oscillator. The sensor and model, both represent significant advances in real-time measurement for peat production and in the analysis of the interaction between the bog and the machine. (C) 2001 Silsoe Research Institute.